The overall objective in this proposal is to optimize the PDT (Photodynamic Therapy) light distribution for application to human prostate cancer using the canine prostate as a model. Photodynamic therapy, a new approach to the treatment and management of prostate cancer as well as other malignant tumors, refers to the process of the excitation of a photosensitizing drug, which subsequently mediates the production of chemically destructive singlet oxygen. Adenocarcinoma of the prostate is a significant problem. Traditional approaches to treatment are not fully satisfactory. A new and promising treatment modality, such as PDT, would be a welcome adjunct to the traditional modes of therapy. This application proposes a comprehensive program to develop all major aspects needed to apply PDT to a specific clinical problem. No such program now exists for the use of PDT in the clinical setting. This will benefit the cancer patient and provide for a more accurate evaluation of the PDT treatment mode, as well as establishing the pattern for future systematic approaches to treatment of other tumor types by PDT. To accomplish this goal we intend to: (A) Characterize and compare the optical properties of normal and tumor prostate tissues at wavelengths of 630 nm - 800 nm using excised Canine and Human tissue, and in-vivo Canine tissue. (B) Assess whether a predictable and controlled volume of necrosis can be produced, using single fiber geometries, in normal and tumor prostate tissue by limited optical and photosensitizer measurements in individual subjects. (C) Establish threshold PDT irradiation parameters to limit damage to adjacent normal tissue during treatment. (D) Develop strategies for the extension of single fiber techniques to multiple fiber irradiation in irregular target tissue geometries. (E) Apply these methods to a veterinary trial of PDT in spontaneous dog prostate cancer. This research promises to bring a new therapeutic tool to bear on a form of cancer which cannot always be successfully treated by traditional means. A successful conclusion to this study will set the stage for an improved methodology for treatment of human prostate carcinoma.